Methods have been known in which blood cells, i.e. leukocytes, reticulocytes, erythrocytes and the like are rapidly measured by using a principle of flow cytometry.
As one of such measurement methods, for example, U.S. Pat. No. 6,114,173 discloses a method for counting and detecting reticulocytes, erythrocytes and platelets in whole blood samples as well as a reagent composition used for the method. Specifically, reticulocytes are stained with a reagent mixture containing a cationic dye, particularly Oxazine 750, and their scattered light signal and light absorbance signal are measured using flow cytometry. Then, erythrocytes and reticulocytes in blood samples are differentiated by the difference in absorbance signals, and the group of erythrocytes and reticulocytes and platelets are differentiated by the difference in scattered light signals, so as to determine total numbers of each species.